1. Field of the Invention
The present invention generally relates to the molding of containers for liquid and viscous products. More particularly, the invention relates to a system and method for hydraulic blow molding of a container from a preform.
2. Description of Related Art
Plastic containers are commonly used for the packaging of various products, including liquid products and viscous product. One of the most common forms of plastic container is the blow molded plastic container, which are often formed of polyester materials and, more specifically, polyethylene terephthalate (PET). Blow molded plastic containers are typically formed by placing a heated preform into a blow mold and then inflating the preform with air until the preform contacts the interior surfaces of the mold cavity, which define the final shape of the desired container. Once the inflated preform has been held against the interior surfaces of the mold cavity by the pressure of the blow air for a length of time sufficient to “freeze” the plastic, the molded container is removed from the mold.
The molded containers are then transported to the location where the container will be filled with the intended product. This may include the packaging and shipping of the container to a remote location or may involve the transfer of the container to a local facility where these final steps occur before the finished product is shipped to a retailer or end-user.
With the above method, blow molding and filling are distinct and separate steps in the process of producing a product filled container. A newer process involves the use of the product in the molding of the container. Instead of utilizing air as a blowing medium, this new process utilizes a liquid, and more specifically the actual product being packaged in the container and sold to the end consumer, as the container's molding medium. As used herein, this type of molding is referred to as hydraulic blow molding.
In traditional blow molding, after the heated preform has been introduced into the mold cavity, a stretch rod is often advanced within the preform to initiate longitudinal stretching of the preform before any significant radial expansion of the preform is undertaken by the introduction of blow air. The stretch rod will typically remain within the preform during radial expansion, and is retracted prior to removal of the resultant container from the molding machine.